1. Field of the Invention
The present invention relates to an optical axis conversion lens which is used in a fine optical element having a light guide and which can freely change an optical axis of light emitted from the light guide without being limited by the height of the light guide.
2. Description of the Prior Art
Generally, light emitted into space from a light guide has lost the effect of being confined by the light guide and is diffused in the thickness direction of the light guide. Conventionally, when converting the emitted light from a light guide into light beams in space which have a narrow spread angle, the diffusion is normally suppressed by disposing a conventional lens or a cylindrical lens a rotational symmetry in proximity to an end face of the light guide.
An example of the conventional technique is provided in JP-A 10-9813. FIG. 4 is a perspective view of an optical position detector which uses a conventional bar shaped lens as disclosed in JP-A 10-9813. In FIG. 4, 101 is a substrate, 102 is a buffer layer, 103 is a first slab light guide, 104 is an input optical fiber, 105 is an optical fiber support, 106 is a first slab light guide end face which has a predetermined curved surface, 107 is a light emerging end face of the first slab light guide 103, 108 is a bar shaped lens which is used as an optical means having a uni-axial focussing operation. The bar shaped lens 108 is supported by the bar shaped lens support and is fixed to the substrate 101. 110 is a surface to be detected, 111 is a second slab light guide, 112 is a light incident end face of the second slab light guide 111, 113 is a second slab light guide end face which has a predetermined curved surface, 114a and 114b are branched light guides connected to the second slab light glide 111. 115a and 115b are output optical fibers, and X. Y. Z are rectangular coordinate axes.
The curvature of the first slab light guide end face 106 and the bar shaped lens 108 is determined so that the light beams converged by them have a focal point at approximately a central position in a desired measurement range of the detected surface 110. Furthermore, the position of the second slab light guide end face 113 and the bar shaped lens 108 is determined so that the second slab light guide end face 113 is in the focal position of the reflected light from the detected surface 110 which is converged in the Y-axis direction by the bar shaped lens.
The operation of conventional bar shaped lens will be discussed below.
Light introduced from an input optical fiber and reflected by a first slab light guide end face 106 is emitted from a light emerging end face 107 and reaches the detection surface 110 after passing through the bar shaped lens 108. The light beam reflected from the detection surface 110 enters the bar shaped lens 108 again and is introduced into the second slab light guide 111 from the incident end face 112. Then, an image of the light beam is formed at the branching point of the branched optical guides 114a and 114b and are output from the output optical fibers 115a and 115b. 
Since a conventional optical axis conversion lens is constructed as above, when the height of each slab light guides 103 and 111 is limited by the diameter of the optical fibers 104, 115a, 115b or the like, the diameter of the bar shaped lens 108 is limited by the height of the slab light guides 103 and 111. In other words, it is necessary to limit the diameter of the bar shaped lens 108 so as to be the same as that of the optical fiber 104, 115a, and 115b. Thus, the problem has arisen that the diameter of the bar shaped lens is reduced and the focal distance becomes too short, so a narrow beam is not obtained at a position far away from the slab light guide.
The present invention is proposed to solve the above problems and has the object of providing an optical axis conversion lens which can freely convert the optical axis of light emerging from a light guide without being limited by the height of the light guide and which can form a narrow beam even at a position far away from the light guide.
An optical axis conversion lens of the present invention is provided with a light incident/emerging surface, a light converging cylindrical surface which converges either light emitted to an external space or incident light from the external space in one direction, and an internal reflection mirror which aligns the optical axis of the light incident/emerging surface with an optical axis of the light converging cylindrical surface.
In this way, it is possible to freely convert the optical axis of light emerging from the light guide without being limited by the height of the light guide and to form a sufficient narrow beam even at a position far away from the light guide. In addition, the optical axis of incident light from an external space may be freely converted and may be introduced into the light guide.
According to the present invention, the optical axis conversion lens is arranged on a light guide end face which emits light beam with a spread angle of xcex8, the aperture width of the lens is formed so as to be approximately equal to the optical distance between the principal plane of the lens and the light guide end face divided by the tangent of the spread angle xcex8 and so as to be larger than the thickness of the light guide.
In this way, it is possible to introduce the light beam into the lens while controlling the diffusion of the light.
The optical axis conversion lens of the present invention may be manufactured by using a thick film resist lithography process and a molding process.
In this way, it is possible to mass-produce the optical axis conversion lenses with fine structure.
In the present invention, a lens, which can sufficiently control the diffusion of light beam, is manufactured by using a thick film resist lithography process and a molding process.
In this way, it is possible to mass-produce the lenses which can sufficiently control the diffusion of the light beam even with fine structure.